The Vermont senator’s announcement makes former vice president Mr Biden the presumptive Democratic nominee to challenge President Donald Trump in November.

Mr Sanders plans to talk to his supporters later on Wednesday.

Mr Sanders initially exceeded sky-high expectations about his ability to recreate the magic of his 2016 presidential bid, and even overcame a heart attack last October on the campaign trail.

But he found himself unable to convert unwavering support from progressives into a viable path to the nomination amid “electability” fears fuelled by questions about whether his democratic socialist ideology would be palatable to general election voters.

Today I am suspending my campaign. But while the campaign ends, the struggle for justice continues on. https://t.co/MYc7kt2b16

The 78-year-old senator began his latest White House bid facing questions about whether he could win back the supporters who chose him four years ago as an insurgent alternative to the party establishment’s choice, Hillary Clinton.

Despite winning 22 states in 2016, there were no guarantees he would be a major presidential contender this cycle, especially as the race’s oldest candidate.

Mr Sanders, though, used strong polling and solid fundraising — collected almost entirely from small donations made online — to more than quiet early doubters.

Mr Sanders amassed the most votes in Iowa and New Hampshire, which opened primary voting, and cruised to an easy victory in Nevada — seemingly leaving him well positioned to sprint to the Democratic nomination while a deeply crowded and divided field of alternatives sunk around him.

But a crucial endorsement of Mr Biden by influential South Carolina Representative Jim Clyburn, and a subsequent, larger-than-expected victory in South Carolina, propelled the former vice president into Super Tuesday, when he won 10 of 14 states.Joe Biden preparing for a Democratic presidential primary debate with Bernie Sanders, who has announced he is suspending his campaign (Evan Vucci/AP)

In a matter of days, his top former Democratic rivals lined up and announced their endorsement of Mr Biden.

The former vice president’s campaign had appeared on the brink of collapse after New Hampshire but found new life as the rest of the party’s more moderate establishment coalesced around him as an alternative to Mr Sanders.

Things only got worse the following week when Mr Sanders lost Michigan, where he had campaigned hard and upset Mrs Clinton in 2016. He was also beaten in Missouri, Mississippi and Idaho the same night and the results were so decisive that Mr Sanders headed to Vermont without speaking to the media.

Mr Sanders had scheduled a rally in Ohio but cancelled it amid fears about the spread of coronavirus — and the outbreak kept him home as his campaign appeared unsure of its next move.

The senator addressed reporters the following day, but also sounded like a candidate who already knew he had been beaten.

“While our campaign has won the ideological debate, we are losing the debate over electability,” Mr Sanders said then.

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